Roof secondary water barrier for site-built single-family residential structures. A secondary water barrier shall be installed using one of the following methods when roof covering is removed and replaced:
In High Velocity Hurricane Zone:
a) All joints in structural panel roof sheathing or decking shall be covered with a minimum 4-inch- (102-mm_) wide strip of self-adhering polymer-modified-bitumen tape applied directly to the sheathing or decking. The deck and self-adhering polymer-modified-bitumen tape shall be covered with one of the underlayment systems approved for the particular roof covering to be applied to the roof.
b) The entire roof deck shall be covered with an approved, asphalt-impregnated Type 30 felt underlayment or approved synthetic underlayment installed with nails and tin-tabs in accordance with Sections R4402.7.2, R4402.7.3 or R4402.7.4 of the Florida Building Code, Residential. (No additional underlayment shell be required over the top of this sheet.) The synthetic underlayment shall be fastened in accordance with the manufacture's recommendations.
Outside the HVHZ:
a) The entire roof deck shall be covered with an approved self-adhering polymer-modified-bitumen sheet meeting ASTM D 1970 or an approved self-adhering synthetic underlayment installed in accordance with the manufacturer's installation instructions. No additional underlayment shall be required on top of this sheet for new installations.
b) An underlayment system approved for the particular roof covering shall be applied with the following modifications:
(1) For roof slopes that require one layer of underlayment, a layer of approved asphalt-impregnated ASTM D 226, "Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing'" Type I or Type II underlayment shall be installed. The felt is to be fastened with 1-inch (25-mm) round plastic cap or metal cap nails attached to a nailable deck in a grid pattern of 12 inches (305mm) staggered between the over-laps with 6-inch (152-mm) spacing at the overlaps. The synthetic underlayment shall be fastened in accordance with the manufacture's recommendations.
(2) For roof that requires two layers of underlayment, an approved asphalt-impregnated ASTM D 226 Type I or Type II underlayment shall be installed in a shingle-fashion and lapped 19 inches (483 mm) and fastened as described above. An approved synthetic underlayment shall be installed in accordance with the manufacture's installation instruction. (No additional underlayment shall be required over the top of this sheet).
Scientists are testing code-approved tar-paper products and synthetic and self-adhered roof underlayments to determine how each performs against high winds and wind-driven rain.
One way to achieve this is to reduce or eliminate water intrusion through the roof sheathing when the primary roof covering of asphalt shingles, metal and felt paper blows off or wind-driven rain is forced between the roof covering and roofing felt or underlayment.
Synthetic roof underlayments are increasingly being adopted because they outperform Type 15 and 30 tar paper in wind and UV resistance. Synthetics are less expensive to install and don't deteriorate or absorb moisture like tar paper.
Armed with testing data currently available from the Washington-based International Code Council, the Florida Building Code and Miami-Dade County on certain synthetic roof underlayments, the insurance industry has begun to look outside Florida. As an example, Baldwin County, Ala., is approximately 20 miles (32 km) from Mobile, Ala., out-lawed the use of tar paper almost a year ago. Local code now requires a synthetic or self-adhered roof underlayment. This came after pressure from insurance companies who indicated they would full out of the market or raise rates substantially.
A NATIONWIDE ISSUE
When it comes to high-wind and rain events, Florida and the coastal Southeast are not alone. The winter and spring of 2008 have shown an increase in tornadoes, hail and water damage throughout the Midwest and other regions of the country. Even California experienced tornadoes in January and May. Insurance industry representatives already have begun to approach the ICC in an effort to impact roofing codes across the nation.
While it is relatively inexpensive to incorporate a synthetic roof underlayment, the potential savings to property owners; insurance companies; and state, federal and local governments is enormous.
The reality is that synthetic roof underlayments are a cheap form of long-term protection against water intrusion. The cost to a property owner to repair and replace a 15-by 15-foot (4.6- by 4.6-m) section of metal shingles or standing-seam panels and tar paper that have blown off would cost around $1,000. Add the damage resulting from heavy rain intrusion and costs easily could be tens of thousands of dollars, if not more. Synthetic roof underlayments, mechanically installed with nails or self-adhered, provide superior benefits to all the stakeholders.
These improved roof systems can better withstand high winds and wind-driven rain, providing property owners with additional protection during extreme weather events and allowing them to stay in their homes after such events. This reduces relocation and temporary housing costs and other additional expenses. While it is relatively inexpensive to incorporate a synthetic roof underlayment, the potential savings to property owners; insurance companies; and state, federal and local governments is enormous.
Mark Strait is president of Kirsch Building Products LLC, Simi Valley, Calif.